Illustris-1-Dark has the LHaloTree merger trees available. The tree contains the connectivity
between progenitors and descendants across different snapshots, as well as most important properties from
the Subfind group catalogs.

Illustris-1-Dark does not currently have the Consistent Trees (Rockstar) merger trees available.

Note: Extracting sub-trees for individual galaxies or halos

The merger trees are generally quite large. If you are interested in making a galaxy/halo selection
based on a complex criterion related to assembly history, merger history, etc, then you will need to
download the full tree files. If, however, you are only looking to study the merger history of a few
galaxies/halos, you should instead consider extracting sub-trees on the fly using the
Web API.